Metal treatment and product



Patented June 10, 1941 UNITED 2,244,740 Mar-Ar. TREATMENT AND PRODUCT Robert B. Tanner, Detroit, Mich.

No Drawing. Application May 9, 1939,

- Serial No. 272.722

3Claims.

- This invention relates to the treatment of ferrous surfaces for the purpose of increasing adhesion and corrosion resistance of subsequently applied paint films. It is well known that when untreated steel is painted and an abrasion of v the finish exposes the metal underneath, corrosion takes place and the paint around the exposed area rapidly loses adhesion, either through the formation of rust underneath or because of a generation of alkali onthe metal surfaces, which although perhaps not accompanied by rust will also cause paint failure. A great majority of metal, chemically treated to increase paint adhesion, has been given an insoluble phosphate coating. The process involves first cleaning the metal. after which it is either immersed in, or sprayed with a hot phosphate solution for periods suiilcient to produce a satisfactory surface coating. The articles are then water rinsed to remove any soluble salts. If they were treated with phosphate coating solutions containing nitrate or nitrite they are then given a rinse in a dilute solution of chromic acid. They are then placed in an oven for drying. A large amount of equipment is necessary in carrying out this process as well as considerable heat.

The object of this invention is to provide a simplified method of treating ferrous metals in order to increase paint adhesion. This object is accomplished by making use of an acid material which may be applied simply by brushing, or with a spray gun, and which is left on the surface and dried in situ. The material used makes it possible to treat the metal with only a small outlay of equipment and with a reduction in the number of operations. The present process is carried out by making use of solutions of am- 'monium acid fluoride. The metal is cleaned of oil, drawing compounds, and other foreign material and is then ready for treatment.

The following examples are given by way of illustration and not limitation, it being understood that wide deviations are possible in ingredients, proportions, temperatures, etc., without departing from the spirit of the invention:

Example No. 1

A 15% solution of ammonium acid fluoride containing 1% of Duponol WA paste (trademark) a wetting agent manufactured by the E. I. du Pont de Nemours & Company of Wilmington, Delaware, containing sodium lauryl sulphate, was sprayed at room temperature of 75 1". onto a ferrous metal object so that the surface was uniformly wetted. The article was then dried in an oven for two minutes at 300 F. After cooling, the article was ready for painting without further treatment.

Example No.2

A 5% solution of the acid salt, without a wetting agent, was used to' wet the surface of a steel panel. The panel was set aside at room temperature until dried.

Example No. 3

A 10% solution without a wetting agent was applied the same as in the above example after which the article was baked for 10 minutes at 550 F.

Example No. 4

A ferrous article was treated with a solution the same as in Example No. 1 and dried for 10 minutes at F.

Following the above procedure the articles were given two standard coats of black baking enamel and subjected to salt spray tests. Following these tests it was discovered that the treated articles were highly superior tountreated articles which had been enameled and tested in the same manner. Although the baking step is not necessary, it is usually advisable in order to shorten the interval before paint may be applied. In general, the higher the concentration of the ammonium acid fluoride used, thebetter the paint adhesion under corrosive conditions. Boththe baking temperature and time may be varied over a considerable range without deleterious results. Where desired, the article may be dipped in a solution of the acid fluoride to wet the surface. The acid fluoride may also be applied over chemically produced coatings on ferrous surfaces to increase paint adhesion under condtions substantialiy the same as indicated in the examples and with variations permissible as noted. The ammonium acid fluoride solution should dry upon the metal surface and remain there, since its removal will defeat the purpose of the treatment.

The present invention is especially applicable in instances where lack of floor space, or the expense, prohibits the installation of equipment necessary for more involved systems of metal treatment, since the present method may be carried out very cheaply and simply. This method may also be used on stationary objects where it would be impossible to process them in a tank or run them through a conveyor system, such as is customary in commercial practice, since the ammonium acid fluoride may be applied and dried without the necessity of any application of heat.

I claim: 1. The method of treating ferrous metal articles to increase paint adhesion which comprises subjecting said articles to the action of an aqueous solution of ammonium acid fluoride and drying the same upon said surfaces.

2. The method of treating ferrous metal articles to increase paint adhesion which comprises subjecting said articles to the action of an aque ous solution of ammonium acid fluoride in comsaid continuous coating.

' ROBERT R. TANNER. 

